The invention relates to a gas-blast electrical circuit breaker comprising:
a sealed casing filled with high dielectric strength insulating gas, notably sulphur hexafluoride,
a pair of separable contacts having a stationary or semi-stationary contact and a movable contact designed to be moved by an operating means between a closed position and an open position,
a breaking gap with formation of an arc between the separated contacts,
and a gas-blast device capable of generating a gas outflow to the breaking gap to cool the arc by convection.
In state-of-the-art SF6 piston compression circuit breakers, cooling of the arc before zero current is performed by convection by replacing a certain quantity of hot gas with cold gas. In the vicinity of zero current, cooling of the arc is achieved mainly by radial conduction. It can be noted that convection and conduction are the two main heat exchange modes. The heat exchange by radiation is very low during breaking of a low intensity arcing current. During the high arcing current period, the heat exchange by radiation becomes great, and subjects the puffer nozzle to high heat stresses. The opaque nozzle is generally made of polytetrafluorethylene loaded with alumina. Manufacturing of a nozzle of this kind is achieved by machining.
The object of the invention consists in improving the breaking performances of an SF6 gas-blast circuit breaker.